1. Field of the Invention
The present invention relates to measuring signals in systems, and in particular, measuring high frequency signals in integrated systems.
2. Description of the Related Art
A major problem in testing integrated high frequency systems such as radar systems, test equipment systems and the like, is isolating defective or substandard circuits. Typically, an integrated high frequency system may consist of between approximately 30 and 40 circuits or components. Often, the multiple circuits in these complex high frequency systems may make it difficult to isolate a defective circuit.
However, combining many functions or circuits on one substrate and/or housing in an integrated high frequency system is cost effective and reduces the overall size of the system. Typically, circuits and respective connections to other circuits are formed using traces on a substrate. For example, microwave transmission lines made out of TEFLON fiberglass may be formed on a substrate to electrically connect circuits. As many as 40 circuits may be manufactured on one substrate using the TEFLON fiberglass. For example, switches, filters, amplifiers, matching networks, bias tees, antennas and pads, all may be manufactured onto a single substrate.
Often a high frequency system designer will breadboard each circuit in a respective housing in order to optimize the design. This process is complicated, time consuming and expensive. Housed circuits must be connected by coaxial cables and expensive drivers, then must be designed and manufactured for each circuit. A typical test assembly of circuits, housings, drivers and cables used to simulate the integrated high frequency system seldom behaves the same as the final integrated system. The interaction between housed circuits often do not properly simulate the behavior of the final integrated circuits. Also, the connectors and cables between the housed circuits add mismatches that can cause interaction problems between housed circuits that will not be present when the system is integrated.
One proposed solution to measuring high frequency signals in circuits is described in "The K-50L Coaxial Probe: Its Origin, Applications and Benefits," by Robert R. Kornowski, Automatic RF Techniques Group Conference, May 19, 1995 ("Kornowski reference"). The Kornowski reference uses a relatively large "broadband coaxial probe" with multiple telescoping pins to measure "high frequency" signals.
However, the Kornowski reference has many disadvantages. First, the probe does not have a corresponding position on a substrate for mounting and thus may not affix securely to a substrate during measuring. Second, the probe is relatively large, and thus highly inductive, which may reduce the accuracy of measured signals. Third, Kornowski teaches a probe which only measures up to approximately 3 GHz.
Therefore, it is desirable to provide an apparatus for measuring high frequency signals in a system. The apparatus should reduce or eliminate the previous costly and complex testing process requiring separate housings, cables, and drivers. The apparatus should be easy to use and accurately Measure high frequency signals from integrated circuits. The apparatus should also not require complex telescoping pins and affix securely to a substrate during measuring. The apparatus should be relatively small in order to reduce inductance which may affect the accuracy of the measured signal. Further, the apparatus should be able to measure a high frequency signal greater than 3 GHz.